Coronary artery bypass graft (CABG) surgery has become a well known and conventional procedure, often referred to as xe2x80x9cheart bypassxe2x80x9d surgery. Such surgery is performed to relieve a condition in which a partially or fully blocked artery is no longer effective to transport blood to the heart and involves removing a portion of a vein from another part of the body, frequently the saphenous vein, to use as a graft and installing this graft at points which bypass the obstruction to restore normal blood flow to the heart. Common though this procedure has become, it is nevertheless lengthy, traumatic and subject to patient risk. Among the risk factors involved is the use of cardiopulmonary bypass equipment, i.e., the so-called xe2x80x9cheart-lung machine,xe2x80x9d to both pump blood and oxygenate the blood so that the patient""s heart may be stopped during the surgery, with its function performed by the cardiopulmonary bypass equipment.
Prior to the present invention, it has been found possible to conduct CABG surgery without stopping the heart, i.e., on a beating heart. In such a beating heart procedure, the function of the heart is maintained and the cardiopulmonary bypass equipment is not needed to replace that function. However, since the heart is beating in such a procedure, the surgeon must cope with the movement of the heart, whether the surgery is a bypass procedure or any other type of coronary surgery. Thus, it would be highly advantageous to perform coronary surgery on a stopped heart, but without causing the patient to endure the lengthy, traumatic and risky procedure involved in supporting the patient on cardiopulmonary bypass equipment. The present invention addresses this problem.
The performance of coronary surgery on the beating heart is described by Benetti et al in xe2x80x9cCoronary Revascularization With Arterial Conduits Via a Small Thoracotomy and Assisted by Thoracoscopy, Although Without Cardiopulmonary Bypassxe2x80x9d, Cor. Buropatum, 4(1):22-24 (1995), which is incorporated herein by reference and by Westaby, xe2x80x9cCoronary Surgery Without Cardiopulmonary Bypassxe2x80x9d in the March, 1995 issue of the British Heart Journal which is incorporated by reference herein. Additional discussion of this subject matter can be found in Benetti et al, Chest, 100(2) :312-16 (1991), Pfister et al, Ann. Thorac. Surg., 54:1085-92 (1992), and Fanning et al, Ann. Thorac. Surg., 55:486-89 (1993). These articles discuss the further details of grafting by anastomosis of a saphenous vein or mammary artery to diseased coronary arteries including the left anterior descending artery (LAD) or the right coronary artery (RCA), temporary occlusion of the coronary artery to provide a bloodless anastomotic field, use of a double suture placed above and below the point of anastomosis, and use of a running suture for the anastomosis. These articles also contrast the beating heart procedure to the more widely used CABG method performed on the non-beating heart with cardiopulmonary bypass.
In heart surgery performed while the heart is beating, the surgeon is faced with a moving organ which places increased demands on his skill in performing the desired procedure, e.g., an anastomosis of the left anterior descending artery (LAD) to the internal mammary artery (IMA), or anastomosis of both ends of a free graft means to a target artery and a coronary artery. If, without substantial harm to the patient, the heart could be momentarily substantially stopped or slowed while the surgeon performed the desired task, e.g., taking a stitch or stitches with a suturing needle, such a task would be less difficult to accomplish.
The intentions of the present invention are to provide a surgical procedure in which the heart is momentarily substantially stopped or slowed in a predictable and reliable manner to facilitate the surgery, by electrically stimulating the vagus nerve. This stimulation can be accomplished by first gaining access to the vagus nerve in the chest preferably via the thoracotomy used in the surgery, or in the neck through endoscopic procedures or through a small incision. A suitable electrical stimulating device is then used to briefly apply electric energy to the vagus nerve. For example, separate continuous electrical pulse trains of 10 or less seconds may be intermittently applied to the nerve with, for example, 30 second rest periods between each stimulation. A 50 millihertz current may be used, but the present invention is not limited to any particular quantitative amount of electrical energy. The present invention further provides associated apparatus in the form of various clip or probe means for efficiently electrically coupling the nerve stimulating device or insulated pacing wires to a patient""s vagus nerve.
The time of the stimulation and amount of current applied will vary according to the type of surgery and the nature of the task for which the substantial stopping or slowing of the heart is desired. In any event, the normal sinus rhythm of the heart is rapidly restored by natural forces once the stimulation is terminated. Thus, for repetitive tasks such as stitching during suturing, the stimulation may be repeatedly applied for brief intervals during which time the task can be performed under less difficult conditions than would apply if the heart were beating in a normal manner.
For reasons of safety, one or more heart pacing devices, such as a Pace port-Swann pulmonary artery catheter, may be inserted in conventional fashion to the patient""s heart and used to restore the beating of the heart during the surgery in the event the heart is slow to revive after a nerve stimulating signal is turned off.
The role of the vagus nerves in the control of cardiac rate and rhythm has been recognized for more than three centuries. Furthermore, soon after electrical stimulating devices became available, it was shown that vagal stimulation caused a reduction in heart rate and, as earlier as 1897, Hunt carried out a quantitative study of the effects of vagal stimulation on heart rate; see, for example, Hunt, R., xe2x80x9cExperiments on the Relation of the Inhibitory to the Accelerator Nerves of the Heartxe2x80x9d, J. Exp. Med. 2:252-279 (1897). An excellent discussion of this phenomenon is found in Chapter 4, Parasympathetic Control of the Heart, by Levy and Martin, in Nervous Control of Cardiovascular Function, edited by Randall, Oxford University Press (1984), which is incorporated by reference herein. However, in spite of the fact that the effect of vagus nerve stimulation on heart rate has long been known, it is believed that this knowledge has not previously been applied to coronary surgery. Rather, vagus nerve stimulation for other purposes has been employed, e.g., as disclosed in the Schwartz U.S. Pat. No. 5,330,507 where vagus nerve stimulation is used in connection with treating arrhythmias, and in the Kendall U.S. Pat. No. 5,458,625 which addresses the use of vagus nerve stimulation for the alleviation of substance withdrawal symptoms or the provision of pain relief, stress relief, and/or general muscle relaxation.
Thus, the present invention is believed to be the first use of vagus nerve stimulation to facilitate coronary surgery, wherein heart motion purposely is stopped or slowed for preselected momentary periods of time during the coronary surgery without need for cardiopulmonary bypass support.